JPS5836632B2 - Power plant pulverizer control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power plant, particularly a control device using a coal pulverizer in a power plant.

In the operation of a coal-fired power plant, coal is fed to a pulverizer where it is finely ground and mixed with the primary air stream.
Sent to Burna.

In many cases, the inlet hot/cold mixed air flow is varied by adjusting the opening of a damper to maintain the primary air/coal mixed flow at the desired pulverizer exit temperature.

Furthermore, the total primary air ventilation is usually adjusted to a set value by adjusting the opening of the damper.

One example of conventional equipment is a hot air damper and! The cold air dampers move in the same direction when adjusting the airflow rate, and move in the opposite direction when adjusting the outlet temperature.

When the coal feeding rate changes in response to changes in the fuel demand (signal) from the boiler control device, the coal feeding rate to the pulverizer changes.

Then, as the amount of pulverized coal carried by the primary air flow begins to change, a pressure drop occurs across the pulverizer, causing a change in air flow and outlet temperature.

For example, as the coal feed rate increases, the amount of pulverized coal begins to rise, causing a greater pressure drop within the pulverizer and beginning to reduce the primary air flow rate and outlet temperature.

The mill controller operates the damper to provide the necessary airflow adjustment during process transients.

In the prior art, pulverizer control has been ineffective because the response time required to adjust the amount of primary air ventilation in response to fuel changes is too long.

In other words, in many existing systems, the ventilation adjustment time is so long that when fuel adjustment is required, undesirable disturbances occur in the boiler outlet steam pressure.

The main reason for this is that the mill controller uses a feedback control loop where adjustments begin after process deviations begin to occur.

Therefore, the time required to change the coal feeding rate, taking into account the effect on the pulverizer process, determines the response time of the conventional pulverizer controller.

Feedforward control can generally avoid process malfunctions and improve process response, but to avoid disturbing the control system, e.g. by preventing a smooth and continuous coal supply to the burner. How can feed-forward control be used to improve mill control response time without depositing fines, i.e., without depositing fines and without suspending too thick coal powder on the milling mechanism? There is no prior art that shows whether it can be used.

This invention was made in view of the above-mentioned conventional problems.
The present invention provides a power plant pulverizer having a variable speed coal feeder, a hot air conduit and a cold air conduit under the control of a hot air damper and a cold air damper, respectively, for supplying primary air through a power plant pulverizer. A control device for the machine; a device for detecting the outlet ventilation temperature of the pulverizer, a device for detecting the ventilation amount of the primary air, and a device for generating a coal feeding speed request signal for the variable speed coal feeding machine. and a device that operates the variable speed coal feeder in accordance with the coal feeding speed request signal, and a device that performs a PI operation in response to the primary air ventilation amount detection device and the primary air ventilation amount setting value generation device to open the cold air damper. a total primary air ventilation rate control device that generates a temperature request signal; an outlet temperature control device that responds to the outlet ventilation temperature detection device and the outlet temperature set value generation device and generates a temperature control signal according to the PI operation; and the coal feeding rate an adder that adds the request signal and the temperature control signal to generate an opening request signal for the hot air damper; and an adder that adjusts the opening of the hot air damper in response to the hot air damper opening request signal and the opening detection signal. and a device that adjusts the opening of the cold air damper in response to the cold air damper opening request signal and the opening detection signal, and the adder is configured to adjust the opening of the cold air damper when the coal feeding speed request signal changes. It is an object of the present invention to provide a control device for a power plant pulverizer, characterized in that the hot air damper is controlled in advance.

Further in the accompanying drawings, FIG. 1 shows a belt or other conventional coal feeder 1 for receiving coal from a coal bunker (not shown).
2 shows a conventional pulverizer 10 having a pulverizer 2.

Generally, the coal is pulverized by rollers (not shown) so that typically at least 80% of the pulverized coal passes through the 200-mesh filter.

The classification section 14 returns the insufficiently pulverized and oversized coal particles to the crushing section for recirculation.

It is necessary to maintain above the minimum primary airflow, as insufficient air can cause pulverized coal to settle in the conveying channel and stick to each other, forming dangerous fuel particles and causing an explosive effect in the burner.

In order to operate the boiler smoothly and safely, in this embodiment, the amount of primary air ventilation is set to a constant value.

This constant value is sufficient to transport pulverized coal and is sufficiently larger than the safe minimum value.

However, this primary air ventilation volume setting value is not large enough to blow up unpulverized and overly thick coal particles upwards from the rollers, preventing sufficient pulverization in the pulverizer and forcing oversized coal particles to be recirculated. do not have.

In this embodiment, the amount of primary air ventilation is controlled to a constant set value, but the amount of primary air ventilation is controlled so that the pulverizer meets the requirements of the boiler in the other application of this invention. It can be a variable value if

Hot air is supplied from a preheater (not shown) through a conduit 16 and is controlled by a variable opening damper 18 .

The cold air is supplied through a conduit 20 and a variable opening damper 2
2.

These mixed flows pass through a primary air conduit 24 in which an air flow detector 26 is installed.

In the pulverizer 10, the primary air stream passes through the crushing section and carries the pulverized coal via the sorting section 14 to the outlet of the pulverizer where a temperature sensor 28 is installed.

The pulverized coal is then conveyed via conduits 30 and 32 to a burner (not shown).

The mill controller 25 includes a conventional coal feed regulator 34 that controls the coal feed rate by a speed demand signal from a suitable fuel controller 36.

Similarly, the ventilation amount controller 38 operates the cold-air damper opening adjuster 40 of the cold-air damper 22 .

The hot air damper opening adjuster 44 is the pulverizer temperature controller 4
20 control signal as well as a coal feed rate request feedforward signal shown at 46.

The transient response of the pulverization process to changes in coal feed rate is greatly and safely reduced by operation of this control device.

That is, the control system predicts the direction of deviations that normally occur in the pulverization process when changes in coal feed rate occur, and immediately takes steps to reduce the process deviations.

Such improvements can be realized in the mill 10 as well as in other known mills having a different design from that shown here.

The structure of the pulverizer control device 25 is shown in detail in FIG.

The temperature controller 42 responds to the temperature setting value 43 and the pulverizer outlet temperature detector 28 to drive the hot air damper opening controller 44 to reduce the pulverizer outlet temperature error to zero using a conventional proportional + integral (PI) controller. ) is preferably a motion controller.

Adder 45 combines the temperature controller signal and the feedforward coal feed rate request signal from fuel controller 36 to provide a single opening request signal to hot air pumper opening controller 44 .

It is preferable to use a PI operation controller as the ventilation amount controller 38.

As shown in the figure, the ventilation amount controller 38 responds to the primary air ventilation amount set value 37 and the primary air ventilation amount detector 26 to generate a control signal that is applied to the cold air damper opening degree regulator 40 as a cold air damper opening request signal. Occur.

The opening degree detectors 51 and 53 are used to satisfy the damper opening degree request signal in the damper opening degree regulators 44 and 40, respectively.

To explain the operation, if there is an increase in the coal feed rate request signal to avoid a drop in the boiler outlet steam pressure, the request signal simultaneously (1) increases the fuel feed rate to the coal feeder 12; (2) For the hot air damper opening degree regulator 44, the hot air damper is opened as a feed forward control operation in anticipation of the influence of the increase in fuel supply speed, and the primary air and pulverizer outlet temperatures are set to predetermined values. to the required opening position to maintain it.

If the hot air damper opening is still at a position that deviates from the ideal opening when a process change is transmitted to the pulverizer outlet, the temperature controller 42 and the air flow controller 38 are interlocked to A feedback control correction operation is performed regarding the feed-forward crawler movement.

Any detected outlet temperature error is detected by controllers 42 and 4.
As a result, the opening degree of the hot air damper is again finely adjusted via 4.

Any detected primary air error will also result in a slight reduction in the opening of the cold air damper via the controllers 38 and 40.

Normally, the small control actions due to loop return are not important, and the overall control response time is greatly reduced by the operation of the present invention while allowing the pulverizer 10 to operate smoothly and stably.

If the coal feed rate request signal decreases, this results in process control behavior that is opposite to that described for the case where the coal feed rate increases.

As shown in FIGS. 4 and 5, it can be seen that improvements have been made in the time response in actual pulverizer tests.

When the coal feeding speed increases at time 0 in Figure 4, the conventional pulverizer cannot follow the set value of 70% for approximately 3 minutes in the primary air ventilation rate, causing turbulence and causing the pulverizer outlet temperature to rise. at approximately 5.5°C (
10'F) descent occurs (occurs after the 1st mark),
The pulverizer outlet pressure and the pulverizer bowl pressure differential after approximately 3 minutes then settle to a high value.

Thus, the transient apparently lasts approximately 3 minutes in the mill.

In the case of the pulverizer 10 of the present invention, the turbulence in the primary air flow rate occurs for about 45 seconds, the outlet temperature drop is limited to about 1.1° C. (2 bars) in 3 minutes, and the pulverizer outlet pressure and The pressure differential in the mill bowl settles in less than 1 minute.

Another embodiment of the invention is shown in FIG.

In this embodiment, a feedforward coal feed rate request signal is provided to reversely operate the hot air damper and cold air damper with respect to coal feed rate changes.

For example, as the coal feeding speed increases, the hot air damper opens further and the cold air damper closes further.

Although this embodiment provides a slower process response to coal feed rate changes than the embodiment shown in FIG. 2, the response speed is still faster than that of the prior art.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a coal pulverizer controlled according to the coal pulverizer according to the present invention, FIG. 2 is a block diagram of the pulverizer control device in FIG. 1, and FIG. 3 is a diagram according to another embodiment of the present invention. FIG. 4 is a block diagram of a modified pulverization control device, showing the steps of the speed of the coal feeder using the feedforward control according to the present invention and the prior art that does not use such feedforward control. 5 is similar to FIG. 4, and is a response graph when the feeder speed decreases stepwise. 10...Fine crusher, 12...Coal feeder,
16, 24, 30, 32... Conduit, 18, 22
... Damper, 25 ... Pulverizer control device, 26 ... Primary air ventilation amount detector, 28.
...Temperature detector, 34...Coal feed regulator,
36...Fuel controller, 38...Airflow rate controller, 40...Cold air damper opening adjuster, 42...
... Temperature controller, 44 ... Hot air damper opening adjuster, 51, 53 ... Opening degree detector.

Claims (1)

[Scope of Claims] 1. Power generation having a variable speed coal feeder and a hot air conduit and a cold air conduit supplying primary air through a power plant pulverizer under the control of a hot air damper and a cold air damper, respectively. A control device for a pulverizer, comprising: a device for detecting the outlet ventilation temperature of the pulverizer, a device for detecting the amount of ventilation of the primary air, and a coal feeding speed request signal for the variable speed coal feeding machine. a device that operates the variable speed coal feeder in accordance with the coal feeding speed request signal; and a device that performs a PI operation in response to the primary air ventilation rate detection device and the primary air ventilation rate setting value generation device to generate the cold air. a primary air total ventilation amount control device that generates an opening request signal for the damper; an outlet temperature control device that generates a temperature control signal according to a PI operation in response to the outlet ventilation temperature detection device and the outlet temperature set value generation device; an adder that adds the coal feeding speed request signal and the temperature control signal to generate an opening request signal for the hot air damper; and an adder that adds the coal feeding speed request signal and the temperature control signal to generate an opening request signal for the hot air damper; and a device that adjusts the opening degree of the cold air damper in response to the cold air damper opening request signal and the opening detection signal, and the adder includes a device that adjusts the opening degree of the cold air damper in response to the cold air damper opening request signal and the opening detection signal. A control device for a power plant pulverizer, characterized in that the hot air damper is controlled in advance when the hot air damper changes.